[Buildroot] [PATCH] makedevs: unlink device nodes before they are created

[Yann E. MORIN <yann.morin.1998@free.fr>]

Arnout, All,

On 2016-11-05 01:14 +0100, Arnout Vandecappelle (Essensium/Mind) spake thusly:
> We use makedevs to create device nodes in the target rootfs. However,
> this can be called several times, e.g. when building several filesystem
> images or when rebuilding. When the script is called the second time,
> the device node already exists so mknod() errors out.
> 
> This wasn't noticed before because fakeroot's mknod() wrapper
> (incorrectly) does _not_ error out when the file exists already. Now
> we switched from fakeroot to pseudo, the problem becomes apparent.
> 
> The simplest solution is to change makedevs to first remove the target
> file before creating it. This is simpler than two alternative
> approaches:
> 
> - Removing the target files before makedevs is called is difficult,
>   because we would have to parse the device table file to find out
>   which files have to be deleted.
> 
> - Silently skipping device creation if it exists already is also easy,
>   but then we really should also check if the device numbers and mode
>   are correct, and that is more complicated.
> 
> The other types don't have to be changed. The 'd' (directory) type is
> already OK because it already only creates directories if they don't
> exist yet. The 'f' (file mode) and 'r' (recursive) types only operate
> on files and directories that exist already.
> 
> Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
> Reported-by: Fabio Estevam <festevam@gmail.com>

NAK: we really do not want that files exist in the target in case they
are configured as device nodes in a dev-table. This should not happen.

That it works now is just an ill side-effect of fakeroot being lenient.
That it breaks with pseudo is good.

The fix is far from trivial, though, but we should handle the situation
via pseudo, and understand why it does not reload its DB.

If we can't fix our use of pseudo, then we should revertt to using
fakeroot for this release cycle.

Regards,
Yann E. MORIN.

> ---
>  package/makedevs/makedevs.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/package/makedevs/makedevs.c b/package/makedevs/makedevs.c
> index cacb144..d477292 100644
> --- a/package/makedevs/makedevs.c
> +++ b/package/makedevs/makedevs.c
> @@ -622,6 +622,7 @@ int main(int argc, char **argv)
>  				for (i = 0; i < count; i++) {
>  					sprintf(full_name_inc, "%s%d", full_name, start + i);
>  					rdev = makedev(major, minor + i * increment);
> +					unlink(full_name_inc);
>  					if (mknod(full_name_inc, mode, rdev) == -1) {
>  						bb_perror_msg("line %d: Couldnt create node %s", linenum, full_name_inc);
>  						ret = EXIT_FAILURE;
> @@ -638,6 +639,7 @@ int main(int argc, char **argv)
>  				free(full_name_inc);
>  			} else {
>  				rdev = makedev(major, minor);
> +				unlink(full_name);
>  				if (mknod(full_name, mode, rdev) == -1) {
>  					bb_perror_msg("line %d: Couldnt create node %s", linenum, full_name);
>  					ret = EXIT_FAILURE;
> -- 
> 2.9.3
> 
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